NITROGEN METABOLISM IN COLD-EXPOSED RATS

Abstract

In these studies, male albino rats were exposed to cold (2–3 °C) for a 7-day period. In vivo studies included the daily measurement of body weight gain, food intake, urine volume, body and liver composition, and nitrogen retention. In vitro, the activities of the following liver enzymes were measured: aspartic acid transaminase, alanine transaminase, arginase, glutamic acid dehydrogenase, and phosphate-activated glutaminase. The results of these experiments demonstrate that exposure of rats to cold increases amino acid catabolism, in part at least to meet increased energy requirements, and reduces protein synthesis as a consequence in the period 2–5 days inclusive, despite a marked increase in food intake. Cold exposure was without effect upon protein absorption but, after 24 hours in the cold, the nitrogen which appeared in the urine increased from about 55% (at 22 °C) to about 76% of the amount that had been absorbed. No effect of cold exposure on nitrogen retention was apparent in the first 24 hours of cold exposure. The subsequent decreased nitrogen retention, on a time basis, appears to bear a relationship to changes in liver enzyme activities, particularly to the increased activities of liver transaminases and arginase.